Highly dispersed metal oxides having electrostatically positive charging capacity are primarily used as constituents in developers, frequently termed toners, for rendering negative electrostatically charged images visible in processes, such as, for example, electrophotography and electrostatic printing, in which a positive charge is adjusted or regulated.
German Offenlegungsschrift DE-OS- No.3 330 380 describes a pyrogenically produced silicon dioxide modified with an ammonium-functional silane which contains a terminal vinyl group and is known as a positive charged controlling agent for toners. In order, however, to achieve a sufficiently hydrophobic surface, the oxide has to be treated simultaneously or subsequently with suitable hydrophobic agents.
In contrast to the process described in German Offenlegungsschrift DE-OS- No. 3 330 380, the process of this invention not only imparts a highly stable and positive triboelectric charge to the metal oxides when they are used as toners, but also simultaneously imparts a highly hydrophobic orientation to the surface of the modified highly dispersed metal oxides.
It is an object of the present invention to provide highly dispersed hydrophobic metal oxides having high, stable, uniform and positive triboelectric charging capacity as a control agent for positive chargeable toners in a single step. Another object of the present invention is to provide a process for preparing highly dispersed metal oxides which are hydrophobic and have high, stable uniform and positive triboelectric charging capacity as a control agent for positive chargeable toners. A further object of the present invention is to provide highly dispersed metal oxides which may be used as a positive charged controlling agent for toners.